The present invention relates to an automatic document feeding device which continuously transfers documents to an information reading position (sheet processing section) in an apparatus of forming an image, such as an electrophotographic copier, and especially, the present invention relates to an automatic document feeding device which can control a document transfer according to document sizes in operating a double-side or duplex process.
In an image forming apparatus, such as an electrophotographic copier, there is used an automatic document feeding device, so-called ADF (automatic document feeder), in order to automatically supply plural documents one by one to a position of reading a content of the document. Recently, the automatic document feeding device is structured such that the ADF can process not only a document having information on one side but also a document having information on both sides.
As the aforementioned automatic document feeding device in which the one-side process and the double-side process can be carried out, for example, there has been known a structure disclosed in Japanese Patent Publication (KOKAI) No. H7-175279 (first prior art). An automatic document feeding device disclosed in this publication is structured such that the documents are stacked sequentially from a top in a paper supply stacker (a top document is page one, a second document is page two, a third document is page three . . . ) in case an one-side process is carried out, and the documents are fed from the top sequentially and supplied to a document reading section through a supply path in a U shape. The documents, information of which have been read in the document reading section, are ejected onto a paper ejection stacker sequentially by a continuous path as they are, so that the documents ejected on the paper ejection stacker are collated as page one, page second, page third . . . from the bottom, resulting in no need of collating the ejected documents.
Also, this automatic document feeding device is structured such that the document is switched back from an ejection path, where one side of the document has been processed, and is guided again to the supply path to carry out the double-side process. However, if the documents in which the double-side processes have been finished are ejected on the paper ejection stacker as they are, it is necessary to collate the documents. Thus, this automatic document feeding device carries out a transfer control to carry out three rotations or circulations passing the document reading section, that is, (reading a front surface of the document)xe2x86x92(reversing the document)xe2x86x92(reading a rear surface of the document)xe2x86x92(reversing the document)xe2x86x92(skipping)xe2x86x92(ejecting the document).
Also, in a structure disclosed in Japanese Patent Publication (KOKAI) No. H8-123103 (second prior art), there are formed a switchback path for switching back a document disposed in a middle of the paper ejection path, and a reverse ejection path for reversing the document directly from the switchback path and ejecting the same on the paper ejection stacker. In this structure, in the double-side process mode, the document in which the double-side process has been completed is ejected from the reverse ejection path to the paper ejection stacker without being supplied from the switchback path to the document reading section. In this publication, there is also disclosed a technology for improving a double-side process speed such that a first document is switched back in the switchback path, and on the way of ejecting the same, reading a second document is carried out while the first document and the second document are overlapped in the switchback path.
Normally, in the automatic document feeding devices as described above, it is necessary to process a large-sized document and a small-sized document in accordance with necessity. In the known automatic document feeding devices described above, in case of transferring the documents, the same process is carried out regardless of the sizes of the documents.
Namely, in the aforementioned automatic document feeding devices, in case processing of the documents is carried out in accordance with the first prior art, after processing of the first document has been finished, a second document is fed out, so that a process speed is slow in case of a small-sized document which requires a high speed processing. Also, in case processing of the documents is carried out in accordance with the second prior art, in the large-sized document which does not require the high speed processing comparatively, there is caused a problem, such as a jamming or paper jam in the switchback path, due to its own weight and size of the large-sized document.
The present invention has been made in view of the foregoing, and an object of the invention is to provide a sheet transferring device, which can carry out an optimum process in accordance with a sheet size in case of operating the double-size process while there is no need of collating the ejected and processed sheets.
Further objects and advantages of the invention will be apparent from the following description of the invention.
An automatic document feeding device of the invention is basically formed of a paper supply path for guiding a document on a paper supply tray onto a platen for processing the document, a switchback path communicating with the paper supply path for switching a transfer direction of the document which has passed above the platen, and a paper ejection path communicating with the switchback path. The paper ejection path reverses a front surface and a rear surface of the document transferred from the switchback path and ejects the document onto a paper ejection tray. The automatic document feeding device further includes detecting means disposed in the paper supply path including the paper supply tray at an upper stream side of the platen to detect a length of the document in a transferring direction, and controlling means electrically connected to the detecting means for controlling a timing of feeding the document into the switchback path in accordance with the length of the document detected by the detecting means.
Namely, in case a document to be read is a small-sized document, a first document and a second document cross each other in the switchback path. And, in case the document to be read is a large-sized document, the first document and the second document do not cross each other in the switchback path.
Accordingly, there is improved a process efficiency for the small-sized document, such as A4 size or letter size, which is used frequently in the device, and the large-sized document can be transferred securely without causing a sheet jam in the switchback path.